Light emitting diode and method for manufacturing the same

ABSTRACT

A light emitting diode and a method for manufacturing the same are disclosed. The light emitting diode comprises: a transparent substrate; a reflective layer located on a surface of the transparent substrate; a solder layer located on the other surface of the transparent substrate; a semiconductor epitaxial structure located on the solder layer, wherein the semiconductor epitaxial structure comprises a n-type contact layer, and the n-type contact layer can be a structure having a continuous flat surface, a structure having a continuous reticulate or bar surface, or a cylinder or prism structure having a discontinuous surface; and a transparent conductive layer located on the n-type contact layer of the semiconductor epitaxial structure.

FIELD OF THE INVENTION

The present invention relates to a light emitting diode and a method formanufacturing the same, and more particularly, to a high-brightnesslight emitting diode manufactured by a wafer bonding technique.

BACKGROUND OF THE INVENTION

Referring to FIG. 1, FIG. 1 illustrates a cross-sectional view of aconventional light emitting diode. The light emitting diode comprises asubstrate 100, a n-type semiconductor buffer layer 102, a n-typesemiconductor contact layer 104, a n-type semiconductor cladding layer106, an active layer 108, a p-type semiconductor cladding layer 110 anda p-type semiconductor contact layer 112 stacked in sequence. The lightemitting diode further comprises a p-type contact pad 114 located on aportion of the p-type semiconductor contact layer 112, and a n-typecontact pad 116 located on the exposed portion of the n-typesemiconductor contact layer 104.

The material of the substrate 100 of a conventional light emitting diodeadopts n-type gallium arsenide (GaAs). The substrate 100 composed ofn-type GaAs can absorb light, so that most of the photons produced bythe active layer 108 of the light emitting diode while emitting towardthe substrate 100 are absorbed by the substrate 100, thus seriouslyaffecting the light emitting efficiency of the light emitting diodedevice.

In order to avoid the issue of light absorbed by the substrate, I.Pollentirer et al. in the Gent university in Belgium disclosed atechnology in the journal “Electronics Letters” about directly bondingthe GaAs light emitting diode wafer to the silicon (Si) substrate afterthe GaAs light emitting diode wafer is stripped off the GaAs substratein 1990. Additionally, the U.S. Pat. No. 5,376,580 (application date:Mar. 19, 1993) filed by Hewlett-Packard Co., U.S.A. disclosed atechnology about directly bonding the AlGaAs light emitting diode waferto the other substrate after the AlGaAs light emitting diode wafer isstripped off the GaAs substrate. However, the U.S. Pat. No. 5,376,580has a disadvantage of low yield caused by the need of considering theconsistency of the lattice direction between the bonding wafers.Furthermore, the U.S. Pat. No. 6,258,699 (application date: May 10,1999) filed by K. H. Chang et al., Visual Photonics Epitaxy Co., R.O.C.disclosed a technology about using metal as a bonding agent after thelight emitting diode wafer is stripped off the growth substrate.However, a disadvantage of the U.S. Pat. No. 6,258,699 is that: thelight emitting diode wafer is easy to peel off after bonding, thuslowering the yield.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a light emittingdiode having a transparent substrate, wherein a surface of the substratehaving a reflective layer with high light reflection. Therefore, theloss of light absorbed by the substrate can be reduced, and the reuse ofthe photons can be provided, so as to increase the quantity of thephotons extracted from lateral sides of the device.

Another objective of the present invention is to provide a lightemitting diode, wherein a n-type contact pad of the light emitting diodeis located on the front side of the device, so that the light emittingdiode has a better current-spreading effect.

Still another objective of the present invention is to provide a lightemitting diode, and a transparent conductive layer can be formed tocover the n-type contact layer after etching, thereby increasing lightextraction efficiency and keeping a better current-spreading effect.

Further another objective of the present invention is to provide amethod for manufacturing a light emitting diode, by stripping off agrowth substrate that absorbs light; and bonding a semiconductorepitaxial structure of the light emitting diode to a transparentsubstrate by using a solder material and a wafer bonding step, after thesemiconductor epitaxial structure is completed. Therefore, the loss oflight absorbed by the substrate can be reduced greatly, and the step ofbonding wafer does not need to consider the direction and disposition ofbonding wafer, thus increasing the yield and reducing the productioncost.

According to the aforementioned objectives of the present invention, thepresent invention provides a light emitting diode comprising: atransparent substrate; a reflective layer located on a surface of thetransparent substrate; a solder layer located on the other surface ofthe transparent substrate; a semiconductor epitaxial structure locatedon the solder layer; and a transparent conductive layer located on thesemiconductor epitaxial structure.

According to a preferred embodiment of the present invention, thematerial of the reflective layer is metal, and the material of thesolder layer is a conductive material or an insulating material that isheat-resistant and has a large thermal conductive coefficient, and thematerial of the solder layer can be organic material or metal.

According to the aforementioned objectives of the present invention, thepresent invention provides a method for manufacturing a light emittingdiode, the method comprising: providing a growth substrate, wherein thegrowth substrate comprises a buffer layer and an etching stop layerstacked thereon in sequence; forming a semiconductor epitaxial structurelocated on the etching stop layer; removing the growth substrate, thebuffer layer and the etching stop layer; providing a transparentsubstrate, wherein a surface of the transparent substrate comprises areflective layer, and another surface of the transparent substratecomprises a solder layer; performing a wafer bonding step to bond thesemiconductor epitaxial structure to the solder layer of the transparentsubstrate; and forming a transparent conductive layer to cover thesemiconductor epitaxial structure.

According to a preferred embodiment of the present invention, after thewafer bonding step is performed, the method further comprises etching an-type semiconductor contact layer of the semiconductor structure tomake the n-type semiconductor contact layer form a non-planar continuousstructure or a discontinuous surface structure, so as to enhancecurrent-spreading effect.

The loss of light intensity resulted from the absorbing of the substratecan be reduced greatly by removing the growth substrate. Besides, theyield can be increased and the production cost can be reduced by using asolder material to perform a wafer bonding step. Furthermore, thereflective layer on the transparent substrate can provide reuse ofphotons to increase the quantity of the photons extracted from thelateral side of the device. In addition, depositing a transparentconductive layer on the etched n-type semiconductor contact layer notonly can increase light extraction efficiency, but also can maintaincurrent-spreading effect.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates a cross-sectional view of a conventional lightemitting diode.

FIG. 2 to FIG. 5 a are schematic flow diagrams showing the process formanufacturing a light emitting diode in accordance with a preferredembodiment of the present invention.

FIG. 5 b illustrates a cross-sectional view of a light emitting diode inaccordance with another preferred embodiment of the present invention.

FIG. 6 illustrates a schematic diagram showing light extractiondirections of a light emitting diode in accordance with a preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention discloses a light emitting diode and a method formanufacturing the same. In order to make the illustration of the presentinvention more explicitly and completely, the following description andthe drawings from FIG. 2 to FIG. 6 are stated.

Among semiconductor light emitting devices, AlGaInP is a verycommonly-used material. Because AlGaInP is a kind of direct bandgapmaterials, appropriately adjusting the ratio of In/(Al+Ga) in theAlGaInP material can make the lattice constant of the AlGaInP materialand the GaAs substrate matched. Adjusting the ratio of Al and Ga in theAlGaInP material can make light emitted between 550 nm (green light) and680 nm (red light) in wavelength. It is very easy to adjust the AlGaInPmaterial on the device epitaxy, so it is easy to obtain emitting lightwith desired wavelengths by a linear method, and AlGaInP is verysuitable for use in manufacturing a light emitting device of visiblelight zone.

Besides, adding the content of Al in AlGaInP material can increase thebandgap of the AlGaInP material, so that the AlGaInP material of high Alcontent is typically used as a cladding layer to confine carriersfalling to a central illuminant layer (which is also called as an activelayer), so as to enhance the injecting efficiency and radiation compoundefficiency of the carriers and form a light emitting diode having adouble heterostructure with high light emitting efficiency. The bandgapof the aforementioned cladding layer is larger than the energy of theemitting photons, so that the cladding layer does not absorb the lightemitting from the active layer.

Referring to FIG. 2 and FIG. 5 a, FIG. 2 to FIG. 5 a are schematic flowdiagrams showing the process for manufacturing a light emitting diode inaccordance with a preferred embodiment of the present invention. In themanufacturing of the light emitting diode of the present invention, asubstrate 200 is first provided, wherein the substrate 200 is a growthsubstrate, and the material of the substrate 200 can be such as n-typeGaAs. A buffer layer 202 and an etching stop layer 204 are grown on thesubstrate 200 in sequence by using such as a metal organic chemicalvapor deposition (MOCVD) method. Next, a semiconductor epitaxialstructure of the light emitting diode is grown by using such as a metalorganic chemical vapor deposition method, so as to grow in sequence an-type semiconductor contact layer 206, a n-type semiconductor claddinglayer 208, a multiple quantum well active layer 210, a p-typesemiconductor cladding layer 212 and a p-type semiconductor contactlayer 214 located on the etching stop layer 204 to form a structure suchas shown in FIG. 2. In the preferred embodiment of the presentinvention, the material of the buffer layer 202 can be such as n-typeGaAs; the material of the etching stop layer 204 can be such as n-typeAlGaInP; the material of the n-type semiconductor contact layer 206 canbe such as n-type GaAs; the material of the n-type semiconductorcladding layer 208 can be such as AlGaInP; the material of the multiplequantum well active layer 210 can be such as AlGaInP/GaInP; the materialof the p-type semiconductor cladding layer 212 can be such as AlGaInP;and the material of the p-type semiconductor contact layer 214 can besuch as AlGaInAsP.

After the semiconductor epitaxial structure of the light emitting diodeis completed, the etching stop layer 204 is removed by such as anetching method to remove the buffer layer 202 and the substrate 200 withremaining the epitaxial structure of the light emitting diode, such asshown in FIG. 3.

At this time, a transparent substrate 300 is provided, wherein thematerial of the transparent substrate 300 can be such as Al₂O₃, ZnSe,ZeO, GaP, or glass, etc. Then, a reflective layer 304 is formed on asurface of the transparent substrate 300 by using such as a depositionmethod, and a solder layer 302 is formed on the other surface of thetransparent substrate 300 by using such as a coating method, adeposition method, or an evaporation method, so as to form a structuresuch as shown in FIG. 4. The material of the reflective layer 304 ispreferably a metal of high light reflectivity, such as Al, Au, Ag, andalloy thereof, and the material of the solder layer 302 is a conductivematerial or an insulating material that is heat-resistant and has alarge thermal conductive coefficient, such as organic material or metal.

Subsequently, the epitaxial structure of the light emitting diode shownin FIG. 3 and the transparent substrate 300 shown in FIG. 4 are bondedtogether by using such as a wafer bonding technology to bond the solderlayer 302 to the p-type semiconductor contact layer 214. It does notneed to consider the direction and disposition of light emitting diodewafer desired to be bonded by using the solder layer 302 composed of thematerial that is heat-resistant and has a large thermal conductivecoefficient to perform the wafer bonding step, so that the yield can beincreased and the production cost can be reduced. Besides, after thetransparent substrate 300 is used to replace the substrate 200, the lossof light absorbed by the substrate can be reduced effectively, and thelight extraction efficiency of the light emitting diode can beincreased. Furthermore, the reflective layer 304 of the transparentsubstrate 300 can provide reuse of photons produced by the multiplequantum well active layer 210, so as to increase the quantity of thephotons extracted from the lateral side of the light emitting diodedevice.

After the wafer bonding of the light emitting diode is completed, atransparent conductive layer 216 is formed to cover the n-typesemiconductor contact layer 206 by using such as an e-gun evaporationmethod, a thermal evaporation method, or a sputtering method, toincrease the light extraction efficiency of the light emitting diode.The material of the transparent conductive layer 216 can be such astitanium (Ti), titanium alloy, titanium oxide or titanium nitride (suchas TiN), tantalum (Ta) oxide (Such as Ta₂O₅) or tantalum nitride,platinum (Pt), platinum alloy, indium tin oxide (ITO), indium oxide, tinoxide, or cadmium tin oxide, etc.

After the transparent conductive layer 216 is formed, a definition stepis performed by using such as a photolithographic method and an etchingmethod to remove a portion of the transparent conductive layer 216, aportion of the n-type semiconductor contact layer 206, a portion of then-type semiconductor cladding layer 208, a portion of the multiplequantum well active layer 210 and a portion of the p-type semiconductorcladding layer 212, so as to expose a portion of the p-typesemiconductor contact layer 214. Then, a n-type contact pad 218 isformed on a portion of the transparent conductive layer 216 and a p-typecontact pad 220 is formed on the a portion of the exposed p-typesemiconductor contact layer 214 respectively or simultaneously by usingsuch as a definition technology comprising deposition, photolithographyand etching, so as to complete the manufacturing of the light emittingdiode, such as shown in FIG. 5 a. Because the doping concentration of an-type semiconductor is greater than that of the p-type semiconductor,the n-type contact pad 218 located on the front side of the lightemitting diode can provide better current-spreading effect.

In order to achieve high light extraction efficiency and increasecurrent-spreading effect, after the epitaxial structure of the lightemitting diode shown in FIG. 3 and the transparent substrate 300 shownin FIG. 4 are bonded, the n-type semiconductor contact layer 222 can befirstly defined by using such as developing and dry etching or wetetching technology, so as to form the n-type semiconductor contact layer222 having an uneven surface. The n-type semiconductor contact layer 222can be etched to expose a portion of the n-type semiconductor claddinglayer 208 or not to expose the n-type semiconductor cladding layer 208.In a preferred embodiment of the present invention, the n-typesemiconductor contact layer 222 can be a cylinder or prism structurehaving a discontinuous surface, or a reticulate or bar structure havinga continuous surface. Next, a transparent conductive layer 224 is formedto cover the n-type semiconductor contact layer 222 by using such as ane-gun evaporation method, a thermal evaporation method, or a sputteringmethod, wherein the material of the transparent conductive layer 224 canbe such as titanium, titanium alloy, titanium oxide or titanium nitride,tantalum oxide or tantalum nitride, platinum, platinum alloy, indium tinoxide, indium oxide, tin oxide, or cadmium tin oxide, etc. When then-type semiconductor contact layer 222 exposes a portion of the n-typesemiconductor cladding layer 208, the transparent conductive layer 224covers the n-type semiconductor contact layer 222 and the exposedportion of the n-type semiconductor cladding layer 208; and when then-type semiconductor contact layer 222 does not expose the n-typesemiconductor cladding layer 208, the transparent conductive layer 224only covers the n-type semiconductor contact layer 222.

Similarly, after the transparent conductive layer 224 is formed, adefinition step is performed by using such as photolithographic andetching method to remove a portion of the transparent conductive layer224, a portion of the n-type semiconductor contact layer 222, a portionof the n-type semiconductor cladding layer 208, a portion of themultiple quantum well active layer 210 and a portion of the p-typesemiconductor cladding layer 212, so as to expose a portion of thep-type semiconductor contact layer 214. Then, a n-type contact pad 218is formed on a portion of the transparent conductive layer 216 and ap-type contact pad 220 is formed on the a portion of the exposed p-typesemiconductor contact layer 214 respectively or simultaneously by usingsuch as a definition technology comprising deposition, photolithographand etching, so as to complete the manufacturing of the light emittingdiode, such as shown in FIG. 5 b.

Referring to FIG. 6, FIG. 6 illustrates a schematic diagram showinglight extraction directions of a light emitting diode in accordance witha preferred embodiment of the present invention. The light emittingdiode of the present invention not only has a light extraction direction1 as the conventional light emitting diode, but also has severalnewly-added light extraction direction 2, light extraction direction 3,light extraction direction 4, light extraction direction 5 and lightextraction direction 6, so that high light output brightness can beobtained.

According to the aforementioned description, one advantage of thepresent invention is that: because the present invention uses a soldermaterial that is heat-resistant and has a large thermal conductivecoefficient to perform wafer bonding of a light emitting diode, and itdoes not need to consider the direction and disposition of bonding lightemitting diode wafer, thereby increasing the yield and obtaining theobjective of reducing the production cost.

According to the aforementioned description, the other advantage of thepresent invention is that: because the GaAs growth substrate is removedand the epitaxial structure of the light emitting diode is bonded on thetransparent substrate, the loss of light resulted from the absorbing ofthe substrate can be reduced greatly, and light extraction efficiencycan be increased.

According to the aforementioned description, still another advantage ofthe present invention is that: because a transparent conductive layer isdeposited on the surface of the light emitting diode wafer afterbonding, thereby increasing light extraction efficiency. In addition,depositing the transparent conductive layer on the n-type semiconductorcontact layer after etching can provide high light extraction efficiencyand obtain better current-spreading effect.

According to the aforementioned description, yet another advantage ofthe present invention is that: because the present invention forms areflective layer on a side of the transparent substrate, the reuse ofthe photons can be provided and the quantity of the photons extractedfrom lateral sides of the light emitting diode device can be increased.

According to the aforementioned description, further another advantageof the present invention is that: because the n-type contact pad of thelight emitting diode of the present invention is located on the frontside of the device, the current-spreading effect of the light emittingdiode of the present invention is better than that of a conventionallight emitting diode whose p-type contact pad is located on the frontside of the light emitting diode.

As is understood by a person skilled in the art, the foregoing preferredembodiments of the present invention are illustrated of the presentinvention rather than limiting of the present invention. It is intendedto cover various modifications and similar arrangements included withinthe spirit and scope of the appended claims, the scope of which shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar structure.

1. A light emitting diode, comprising: a transparent substrate; areflective layer located on a surface of the transparent substrate; asolder layer on the other surface of the transparent substrate; asemiconductor epitaxial structure located on the solder layer; and atransparent conductive layer located on the semiconductor epitaxialstructure.
 2. The light emitting diode according to claim 1, wherein thematerial of the transparent substrate is selected from the groupconsisting of Al₂O₃, ZnSe, ZeO, GaP, and glass.
 3. The light emittingdiode according to claim 1, wherein the material of the reflective layeris a metal having high light reflectivity.
 4. The light emitting diodeaccording to claim 1, wherein the material of the solder layer isheat-resistant and has large thermal conductive coefficient.
 5. Thelight emitting diode according to claim 1, wherein the material of thesolder layer is organic material.
 6. The light emitting diode accordingto claim 1, wherein the material of the solder layer is metal.
 7. Thelight emitting diode according to claim 1, wherein the semiconductorepitaxial structure comprises a p-type semiconductor contact layer, ap-type semiconductor cladding layer, a multiple quantum well activelayer, a n-type semiconductor cladding layer and a n-type semiconductorcontact layer stacked in sequence, wherein the p-type semiconductorlayer contacts the solder layer.
 8. The light emitting diode accordingto claim 7, wherein: the material of the p-type semiconductor contactlayer is AlGaInAsP; the material of the p-type semiconductor claddinglayer is AlGaInP; the multiple quantum well active layer comprises anAlGaInP/GaInP structure; the material of the n-type semiconductorcladding layer is AlGaInP; and the material of the n-type semiconductorcontact layer is GaAs.
 9. The light emitting diode according to claim 7,wherein the n-type semiconductor contact layer is a continuous surfacestructure.
 10. The light emitting diode according to claim 7, whereinthe n-type semiconductor contact layer is a discontinuous surfacestructure, and the discontinuous surface structure is selected from thegroup consisting of a cylinder structure and an prism structure.
 11. Thelight emitting diode according to claim 1, wherein the material of thetransparent conductive layer is selected from the group consisting oftitanium (Ti), titanium oxide, titanium nitride, titanium alloy,tantalum (Ta) oxide, tantalum nitride, platinum (Pt), platinum alloy,indium tin oxide, indium oxide, tin oxide, and cadmium tin oxide.
 12. Amethod for manufacturing a light emitting diode, comprising: providing agrowth substrate, wherein a buffer layer and an etching stop layerstacked on the growth substrate in sequence; forming a semiconductorepitaxial structure on the etching stop layer; removing the growthsubstrate, the buffer layer and the etching stop layer; providing atransparent substrate, wherein a surface of the transparent substratecomprises a reflective layer, and the other surface of the transparentsubstrate comprises a solder layer; performing a wafer bonding step tobond the semiconductor epitaxial structure to the solder layer of thetransparent substrate; and forming a transparent conductive layer tocover the semiconductor epitaxial structure.
 13. The method formanufacturing the light emitting diode according to claim 12, whereinthe material of the etching stop layer is n-type AlGaInP.
 14. The methodfor manufacturing the light emitting diode according to claim 12,wherein the semiconductor epitaxial structure comprises a p-typeAlGaInAsP contact layer, a p-type AlGaInP cladding layer, anAlGaInP/GaInP multiple quantum well active layer, a n-type AlGaInPcladding layer and a n-type GaAs contact layer stacked in sequence, andthe n-type GaAs contact layer contacts the etching stop layer before thestep of removing the growth substrate, the buffer layer and the etchingstop layer.
 15. The method for manufacturing the light emitting diodeaccording to claim 14, wherein after the wafer bonding step, the p-typeAlGaInAsP contact layer contacts the solder layer.
 16. The method formanufacturing the light emitting diode according to claim 14, whereinafter the wafer bonding step, further comprises performing an etchingstep on the n-type GaAs contact layer to make the n-type GaAs contactlayer form a non-planar continuous structure.
 17. The method formanufacturing the light emitting diode according to claim 14, whereinafter the wafer bonding step, further comprises performing an etchingstep on the n-type GaAs contact layer to expose a portion of the n-typeAlGaInP cladding layer to make the n-type GaAs contact layer form adiscontinuous surface structure.
 18. The method for manufacturing thelight emitting diode according to claim 12, wherein the step of formingthe semiconductor epitaxial structure is performed by using a metalorganic chemical vapor deposition method.
 19. The method formanufacturing the light emitting diode according to claim 12, whereinmaterial of the transparent substrate is selected from the groupconsisting of Al₂O₃, ZnSe, ZeO, GaP, and glass.
 20. The method formanufacturing the light emitting diode according to claim 12, whereinthe material of the reflective layer is a metal having high lightreflectivity.
 21. The method for manufacturing the light emitting diodeaccording to claim 12, wherein the material of the solder layer isheat-resistant and has large thermal conductive coefficient.
 22. Themethod for manufacturing the light emitting diode according to claim 12,wherein the material of the solder layer is organic material.
 23. Themethod for manufacturing the light emitting diode according to claim 12,wherein the material of the solder layer is metal.
 24. The method formanufacturing the light emitting diode according to claim 12, whereinthe material of the transparent conductive layer is selected from thegroup consisting of titanium, titanium oxide, titanium nitride, titaniumalloy, tantalum oxide, tantalum nitride, platinum, platinum alloy,indium tin oxide, indium oxide, tin oxide, and cadmium tin oxide. 25.The method for manufacturing the light emitting diode according to claim12, wherein the step of forming the transparent conductive layer isperformed by using a method selected from the group consisting of ane-gun evaporation method, a thermal evaporation method and a sputteringmethod.